1. Field of the Invention
This invention relates generally to apparatus for strapping of packages, bundles and other articles with encircling straps or bands, and more particularly to a system and apparatus for positioning edge protector pads at the edges of a package, article or bundle and maintaining the pads in place during the strapping operation.
2. Background Art
Large and bulky objects often require strapping together a number of similarly shaped items to provide an easily manipulated package for shipping. A traditional method of strapping used metal bands or straps disposed around the bulky items placed together in an ordered relationship. For most hard objects, such as bricks, a metal band does not present a considerable problem when it is tightened around the objects. However, for more pliable or crushable items, i.e. stacks of corrugated cardboard, wood products, such as veneers, plywoods, hardboards, and other products, the metal bands cut into the surface of the outermost items in a stack and often damage those outermost items to such a degree as to make them unusable for their intended purpose. Even plastic bands which have come into more general use are liable to damage easily crushable items, such as stacks of corrugated cardboard.
More recently, it has become general practice to interpose edge protector pads, also called simply edge protectors, between the edges of a package and the encircling strap to protect the package edges from damage.
Automation of the strapping process has necessitated development of an automated mechanism to position the edge protectors onto the edge of a package bundle or stack of items and to retain the edge protectors thereon while the straps are being tightened. As in many manufacturing or industrial processes, a significant goal is to achieve the most cost-effective solution to a particular problem. As applied to edge protector positioning, the goal has been to design a system and apparatus which is effective in maintaining the edge protector position during strapping or banding and capturing the strap or band over a central portion of the edge protector in all instances. Another goal has been a reduction in the cost of the positioning apparatus and also a reduction in the cost of the individual edge protector pads.
An inexpensive material used for edge protector pads is cardboard or laminated paper which has been folded to approximately a 90.degree. angle to fit over an edge of a stack or bundle of items. A continuous edge protector along all the edges of a bundle or stack alleviates the need for precise positioning of the edge protector during the banding process. For example, U.S. Pat. Nos. 3,398,675 and 4,513,864 each disclose a continuous edge protector for protecting the complete edge of a stack, band or coil of materials. However, providing continuous edge protectors for each of four or eight corners of can become an expensive proposition.
Shorter length edge protector pads have been used to reduce the expense involved in packaging bundles or stacks of items, see, for example, U.S. Pat. Nos. 2,630,214, 3,271,925, and 3,995,409. Precise positioning of the shorter length edge protector is a major consideration, because the strap must securely grip the edge protector pad without slipping off when the strap is tightened. If the strap is tightened when the edge protector pad is not centered beneath the strap, tightening of the strap lifts an opposite side of the edge protector which increases the probability that the strap will slip from the edge protector and onto the bundle or stack of items which are being strapped. Strapping over an edge protector which is not properly centered creates uneven pressure of the edge protector on the package edge, and can cause damage thereto.
Various methods for positioning edge protectors have been proposed. U.S. Pat. No. 3,424,077 proposes a labor intensive manual positioning method which is not easily adaptable to automated equipment and which would also be overly expensive in requiring two operators, one for the strapping operation and the other for positioning the pads.
Automated mechanisms for positioning edge protector pads are described in U.S. Pat. Nos. 3,241,287 and 4,587,791. These patents describe edge protector delivery and positioning apparatus. The apparatus described by both of these patents require the magazine in which the edge protectors are stacked to be movable adjacent the package just prior to the strapping process.
Because the edge protector magazine, the delivery and positioning apparatus and the strap delivery apparatus all take up considerable space around the package, the number of straps which can be looped around most packages is limited to two if the strapping is to be performed simultaneously for each package. In many strapping machines, the strapping apparatus, called a strapping head, is disposed in series along a conveyor for delivering the package to be strapped. The limitation in space further limits the number of strapping heads per package edge to two under normal condition because otherwise the edge protector off delivery apparatus interferes with the delivery of the straps. Simultaneous strapping is normally desirable to produce consistently uniform packages and to speed up the packaging process.
Devices made according to the teaching of U.S. Pat. Nos. 3,241,287 and 4,587,791 also require the tolerances of the edge protectors themselves to be exact in the relative lengths and angular spread of the edge protector walls and in the shape of the edge protectors. Thus, to obtain the close tolerance on the edge protectors, the edge protectors provided are injection molded to and are essentially identical in their dimensions.
Similarly, U.S. Pat. Nos. 3,735,955 and 4,877,673 also provide for injection molded edge protectors. Various modifications of injection molded edge protectors are often necessary to provide a capability of centering the strap relative to the edge protector during the strapping process including, for example, a depressed section on the outer edge of an edge protector having angled sides. As the strap is tightened around a package, the angled edge sides of the edge protector guide the strap toward the center of the edge protector. Because the stress on the edge protector is great during the tightening of the strap, the required structural integrity of the edge protector mandates that it be manufactured by an injection molding process.
Injection molding becomes expensive when considering that each strap for a package must loop around four edges, requiring four edge protectors per strap. Many packages require two or more parallel straps and possibly at least one other additional strap in a transverse direction.
A less expensive alternative to injection molded edge protectors are edge protectors comprising short pieces of laminated paper products, such as pieces of cardboard discussed above, that have been bent along a central line transverse to the longer dimension of approximately a right angle. Edge protectors having acceptable characteristics are presently available. However, the tolerances of laminated cardboard edge protectors are not subject to efficient control.
Inexpensive laminated cardboard edge protectors are now available for use, but their use in an automated positioning apparatus has heretofore been limited by the large variability dimensions of the edge protectors. Dimensions of the different lengths of each of the flanged sides of the edge protector typically range from about 13/4" to about 21/4". The nominal length of each leg is 2 inches, i.e. a flat laminated cardboard strip 4 inches long is folded over at its approximate center. That folding process is not precise, however, and 1/4 inch variability in each leg is common. The angle between the two sides may have a typical value from 80.degree. to about 105.degree..
A great range in dimensional variability of the edge protectors is not desirable from the standpoint of automated edge protector delivery and retention apparatus. Mechanisms to transfer edge protectors from an edge protector magazine to the edge of a package for strapping should be capable of accepting the high degree of variability in the available laminated cardboard edge protectors and dispose them under the strap during the strap tightening step with both reliability and efficiency.
Thus, what is necessary is a reliable and accurate edge protector delivery, positioning and retention apparatus which can accept a high degree of variability in the individual edge protectors dispensed from a magazine to continue operation of a strapping device. Another desirable characteristic is the capability of retrofitting the positioning apparatus in existing strapping machines without necessitating the excessive reconfiguration of any existing strapping machine structure. Yet another desirable characteristic which is needed is a compact positioning apparatus for delivery positioning and retention of edge protectors during strapping of a package, which apparatus is narrow enough to permit disposition of at least three of these apparatus in side by side relationship per edge of each package, for retrofitting a strapping machine having at least three strapping heads.